General Cooling Fan question(s)...

[MadSpleen85]

I've never thought much of it besides "oh that is just normal" but it still seems weird. My question is, my cooling fan runs after the car has been turned off, should it run for one period of time? does it depend on the engine temperature as to how long it runs? Should it switch on and then off within 30 seconds?

I have not had any overheating problems, the temperature needle runs just below dead center after I have been running. Thermostat is maybe a year old, coolant was flushed and refilled 2 months ago and my main relay was replaced in the summer before last (replaced with OEM Honda Part.

I checked all the fuses, in both fuse boxes. Looked at a wiring diagram and looking for some sort of fan timer or something, found the Fan Timer Unit. Searched on here and found that is located on the left side behind the dash, so it is not something I want to rip into unless I have too.

Thanks in advance.

[d112crzy]

I've noticed that same behaviour on a lot of cb7's as well.

Mine doesn't do it. Turns off if I turn the car off.

[MadSpleen85]

Yeah, it just always stuck with me as odd. I know Bri (pittcb7grl)'s 92 CB did not do the on and off thing like mine, and I asked Joe (Geist Zero) about his since they are both 91's and he said his does it occasionally.

[F22HB]

Wonder if they do it to help the car not heat-soak so bad after its been brought up to temp then shut off. Mine does this sometimes too but its kindof random.

[batever]

It's normal behavior to cool the engine. My 92 only does it occasionally, however, and only in the summer or after drives of more than 20 minutes. Most cars do it. I believe it's simply run by the thermostat and if the thermo. detects 194 F or higher the fan starts, even if the engine is off. I've heard my fan run quite a while after a long drive in the summer, so I'm guessingthe fan is run simply off the thermostat reading 194 or higher, just like it is while the car is running.

As a method it does seem kind of weird though when you think about it, since the fan is not directly cooling the engine and it's not actively circulating any coolant. it's just cooling the radiator and the water pump is not circulating coolant thru the engine since the water pump doesn't function when the engine is not turning.

I'm wondering if cooling the radiator with the fan may cause a kind of passive circulation effect,with cooler denser coolant sinking in the radiator to the bottom hose and forcing a slow flow through the engine and out the top hose to the radiator, which helps dissipate excess heat from the engine. As the block can still have a lot of latent heat if the engine has been running a while. It would be even more effective if the car could run a coolant pump as well, but I guess that would be an extra part/extra engineering and not worth it on the cost/benefit analysis. Running the fan on the radiator is an easier way to get some of the same effect.


I've read about passive solar systems that run like this, on convective flow created by a heat and fluid density differential between the solar collector and the fluid in the rest of the system that is running through the house. I googled "convective flow" and came up with this little blurb:

There are many situations in which water flow [is] caused by convection [...]. For example, if a boiler is used to make hot water for heating and also domestic hot water, convective flow can cause radiators to become hot. When the pump that circulates water to the radiators is off, but the boiler is hot for making domestic hot water, the hot water in the boiler is lighter than the cold water in the radiators. If the boiler is located lower than the radiators, as most are, hot water can rise up into the radiators while cold water from the radiators goes down into the boiler. If this happens during the summer, the people in the building can be expected to complain loudly.

THE CONVECTION EFFECT

Flow driven by temperature difference is called convective flow, or gravity flow. Before pumps were widely used, hot water heating systems were designed to circulate hot water to radiators by...

...convective flow. the quote stops here because I didn't wanted to pay cash to read the rest of the article--I think it gets the idea/principle across though--flow is driven by a difference in density that is an effect of a heat differential or heat gradient in the fluid.

[alkoholikwun]

my 92 ex used cycle the fan on after i had driven for quite some time then turn off the engine, but i dont think that it does that anymore. than again i havent driven my car in 2-3 weeks (motor swap). plus it seems like since i changed my thermostat the fan doesnt cycle on when i shut my car off.